The present invention relates to a semiconductor component, in particular an MOS transistor having first and second connection zones of a first conduction type, a channel zone of a second conduction type and a drift zone of a first conduction type, the drift zone formed between the channel zone and the first connection zone, and the channel zone formed between the second connection zone and the drift zone, a control electrode formed insulated from the second zone for controlling a conductive channel in the second zone between the second zone and the drift zone, a drift zone of the first conduction type formed between the second zone and the first zone, and at least one compensation zone.
Such a semiconductor component, in the form of a vertical MOSFET, is disclosed, for example, in J. Tihanyi: xe2x80x9cA Qualitative Study of the DC Performance of SIPMOS Transistorsxe2x80x9d, Siemens Forschungs-und Entwicklungsbericht, Vol. 9 (1980) No. 4, Springer Verlag, page 181, FIG. 1c. Such a MOSFET has an n+-doped drain zone in the region of a back of a semiconductor body and an n+-doped source zone in the region of a front of the semiconductor body. The source zone is surrounded in the semiconductor body by a p+-doped channel zone. Extending between the channel zone and the drain zone is an nxe2x88x92-doped drift zone formed adjacently to a pxe2x88x92-doped zone that likewise adjoins the channel zone. A gate electrode insulated from the channel zone allows a conductive channel to be formed between the source zone and the drift zone when a driving potential is applied.
Such a semiconductor component in the form of a MOSFET having an n-doped drain zone, an n-doped source zone surrounded by a channel zone, and an n-doped drift path formed adjacently to a p-doped zone is also disclosed in U.S. Pat. No. 5,216,275 to Chen and by U.S. Pat. No. 4,754,310 to Coe.
Such MOS transistors are distinguished by a low turn-on resistance and a high breakdown voltage.
In the MOS transistors, the source zone and the channel zone are normally shorted by a source electrode, so that the p-doped zone adjoining the channel zone is at source potential. Even when the MOSFET is on, i.e., when a conductive channel has been formed in the channel zone between the source zone and the drift zone and there is a voltage between the source zone and the drain zone, a voltage drop is produced across the drift path. Such a configuration results in a potential difference between the p-doped zone and the drift path that is greatest close to the drain zone and causes a space-charge zone to form in the boundary region between the p-doped zone and the drift path. The space-charge zone can pinch off the conductive channel in the drift path.
German Published, Non-Prosecuted Patent Application DE 198 15 907 C1 discloses a semiconductor component that can be controlled by field effect and has an n-doped drain zone, an n-doped source zone, a p-doped channel zone surrounding the source zone, and an n-doped drift path formed between the source zone and the drain zone, with a number of p-doped zones spaced apart being formed in the drift path. For driving, a gate electrode is provided that is formed to be insulated from the channel zone. If the semiconductor component is off and a voltage is applied between the source and drain zones, a space-charge zone propagates starting from the source zone and progressively takes in the p-doped zones disposed apart in the drift path. As such, these zones and the adjoining regions of the drift zone are depleted, that is to say free charge carriers recombine and depletion of free charge carriers occurs in the drift path, which results in a high breakdown voltage. To turn on the semiconductor component again after it has been off, the p-doped regions disposed on a floating basisxe2x80x94that is to say, those not connected to a fixed potentialxe2x80x94need to be discharged again. To such an end, an injector is provided that injects p-charge carriers into the drift zone, or into the p-doped zones.
It is accordingly an object of the invention to provide a semiconductor component that can be controlled by field effect that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has a low turn-on resistance and a high breakdown voltage and in which pinch-off of the conductive channel in the drift zone is reduced in the on state.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a semiconductor component, including a first connection zone of a first conduction type, a second connection zone of the first conduction type, a channel zone of a second conduction type, the channel zone having a conductive channel, a drift zone of the first conduction type, the drift zone formed between the channel zone and the first connection zone, the channel zone formed between the second connection zone and the drift zone, a control electrode for controlling the conductive channel in the channel zone between the second connection zone and the drift zone, the control electrode insulated from the second zone, at least one compensation zone of the second conduction type, the at least one compensation zone formed in the drift zone and having at least two segments disposed at a distance from one another, and the distance between two adjacent ones of the at least two segments being chosen such that a punch-through voltage between the adjacent segments corresponds at most to a voltage across the drift zone at twice a rated current. Preferably, the distance between two adjacent segments is chosen such that a punch-through voltage between the adjacent segments corresponds to a voltage across the drift zone between a rated current and two times the rated current.
The second connection zone is isolated by the channel zone from the drift zone that, starting from the channel zone, extends up to the first connection zone. In addition, a control electrode is used to form a conductive channel in the channel zone between the second connection zone and the drift zone.
The distance between the two adjacent segments is chosen such that the punch-through voltage between the two segments corresponds at most to the voltage that becomes established when, with these miconductor component turned on, the drift path has a current flowing through it that is twice the rated current and when the temperature of the semiconductor body is preferably no more than 150xc2x0 C.
The rated current is the current at which the semiconductor component is configured for long-term operation. In such a context, the rated current is definitively determined by the housing and its ability to dissipate heat.
In the case of two regions having identical doping and isolated by a complementarily doped region, the xe2x80x9cpunch-through voltagexe2x80x9d is a general term for the value of the potential difference between these regions at which value a space-charge zone starting from one of the two regions takes in the other of the two regions. In absolute values, the punch-through voltage is preferably below 10 V in such a context.
The semiconductor component according to the invention works as an MOS transistor, with the first zone serving as drain zone, the second zone serving as source zone, and the control electrode serving as gate electrode.
With the semiconductor component turned on, those segments of the compensation zone that are disposed on a floating basis in the drift zone, that is to say, the segments that are not connected to the channel zone, assume a potential value that is between the potential on the first connection zone and the potential on the channel zone, or the potential on the second connection zone shorted by the channel zone. The potential difference between these floating segments and the surrounding regions of the drift zone is lower than in the case of the prior art MOS transistors, in which the whole compensation zone is at source potential. Thereby, the xe2x80x9cjunction effect,xe2x80x9d which refers to the conductive channel being pinched off in the drift path, is reduced in the semiconductor component according to the invention.
When the semiconductor component is off, a space-charge zone is formed starting from the second connection zone, or the channel zone, and, as the voltage rises, progressively takes in the segments of the compensation zone that are further away from the channel zone.
In accordance with another feature of the invention, one of the segments of the compensation zone directly adjoins the channel zone.
In accordance with a further feature of the invention, the at least one compensation zone has more than two segments disposed at a distance from one another.
In accordance with an added feature of the invention, the compensation zone is produced in a column form.
In accordance with an additional feature of the invention, one of the segments has a relatively higher doping than an adjacent other one of the segments.
In accordance with yet another feature of the invention, the number of charge carriers of the first conduction type in the drift zone substantially corresponds to the number of charge carriers of the second conduction type.
In accordance with yet a further feature of the invention, in the drift zone, the number of charge carriers of the second conduction type is greater than the number of charge carriers of the first conduction type.
In accordance with yet an added feature of the invention, the number of charge carriers of the second conduction type in the drift zone is greater than the number of charge carriers of the first conduction type.
In accordance with a concomitant feature of the invention, the drift zone has a doping of between 5xc3x971014 cmxe2x88x923 and 5xc3x9710 15 cmxe2x88x923 and the distance between the adjacent segments is between 0.5 and 4 xcexcm. In one embodiment, the drift zone has a doping of 5xc2x71014 cmxe2x88x923 and the distance between the adjacent segments is between 2 and 4 xcexcm. In another embodiment, the drift zone has a doping of 2xc2x71015 cmxe2x88x923 and the distance between the adjacent segments is between 1 and 2 xcexcm. In a third embodiment, the drift zone has a doping of 5xc2x71015 cmxe2x88x923 and the distance between the adjacent segments is between 0.5 and 1.5 xcexcm.
The charge carrier concentrations in the compensation zone and in the regions of the drift zone that surround the compensation zone are preferably matched to one another such that there are approximately the same number of charge carriers of the first and of the second conduction type. As a result, when a reverse voltage is applied and the control electrode is not being driven, the compensation zones and the regions surrounding the compensation zones become fully depleted, that is to say, p-charge carriers migrate to the zone, or to the electrode, which is at the more negative potential and n-charge carriers migrate to the zone, or to the electrode, which is at the more positive potential. When a positive reverse voltage is applied between drain and source, p-charge carriers migrate to the source electrode and n-charge carriers migrate to the drain electrode. The effect of the compensation zone and the surrounding drift zone being depleted is that, when the maximum possible reverse voltage is present, there are no longer any free charge carriers in the drift zone before breakdown is reached, which results in a high breakdown voltage. In a fully depleted state, the potential in the drift path and in the segments of the compensation zone decreases steadily from the connection zone with the higher potential to the connection zone with the lower potential.
If the component is to be turned on again, the control electrode is driven by applying a suitable driving potential, so that a conductive channel forms in the channel zone. When the component is turned on again and a voltage is applied between the first and second connection zones that is lower than the voltage in the off case, the segments of the compensation zones, which are formed on a floating basis in the drift zone, initially remain charged because there are no free charge carriers present in the segments of the compensation zones.
In such a context, if the voltage difference between the channel zone or a segment of the compensation zone that is connected to the channel zone and a segment of the compensation zone that is disposed at a distance therefrom amounts to the value of the punch-through voltage between these two segments, the potential of the segment disposed at a distance from the channel zone is coupled to the potential of the channel zone. That is to say, the segment disposed at a distance is partially discharged, with its potential initially differing from the potential of the channel zone by the value of the punch-through voltage. If the component includes more than two segments of the compensation zone, this procedure is effected for all adjacent segments.
The individual segments would be discharged in optimum fashion when turning on again if all the segments were connected to the channel zone. However, such a connection results in the aforementioned drawbacks of the prior art, namely that the channel is pinched-off when the component is on.
The dimensioning of the invention, according to which the punch-through voltage corresponds at most to the voltage drop across the turned-on component at twice the rated current and, preferably, at least to the voltage drop across the drift path at the rated current, affords a very good compromise between the demands for rapid discharge of the compensation zones when turning on again and the least possible pinch-off of the channel in the on state. It is also possible to dispense with the use of an additional injector.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor component that can be controlled by field effect, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.